Enhancement of Condensation Heat Transfer, Anti-Frosting and Water Harvesting by Hybrid Wettability Coating

The hybrid wettability coatings have been designed by spraying superamphiphobic SiO2 nano-powder and superamphiphilic gypsum micro-powder with different mass ratio (MR). The condensation heat transfer efficiency, frosting delayed time and water harvesting rate can promote to about 131.50% (MR = 1:0.5), 134.74% (MR = 1:0.5) and 135.62% (MR = 1:1), respectively, although their macroscopical wettability will gradually reduce with the increase in MR. This paper provides substantial insights into the fabrication of efficient superhydrophilic-superhydrophobic hybrid wettability surfaces for condensation heat transfer, anti-frosting and water harvesting applications. Hydrophilic-hydrophobic hybrid wettability structures, inspired by desert beetles, have been widely designed to enhance the dewdrops' migration under subcooled or/and high-humidity environment. However, it is still a challenge to regulate the graded distribution of the hydrophilic micro-regions for condensation applications. In this paper, we design a simple spray method to prepare the superamphiphilic-superamphiphobic hybrid wettability coatings by controlling the mass ratio (MR) of superamphiphobic SiO2 nano-powder and superamphiphilic gypsum micro-powder. We compare the macroscopical wettability, condensation heat transfer efficiency, frosting delayed time and water harvesting rate to demonstrate the unique advantage of hybrid wettability structures. The results show that the condensation heat transfer efficiency, frosting delayed time and water harvesting rate can be respectively promoted to about 131.50% (MR=1:0.5), 134.74% (MR=1:0.5) and 135.62% (MR=1:1), although their macroscopical wettability will gradually reduce with the MR increase. This work will provide substantial insights into the fabrication of efficient superhydrophilic-superhydrophobic hybrid wettability surfaces for condensation heat transfer, anti-frosting and water harvesting applications.